1. Field of the Invention
This invention relates generally to the art of pouring measured quantities of liquids, and more particularly to a low pressure air system for pouring molten metals. In its most preferred embodiment, the system is used for pouring lead straps in the manufacture of batteries.
2. Description of the Prior Art
Several systems presently exist for pouring molten metals, and some systems have been specially adapted for pouring lead, e.g. for use in the construction of batteries. In addition to the problems normally encountered with any molten metal pouring system, special problems exist in the manufacture of lead-acid batteries where lead straps and the like must be poured accurately quickly, efficiently and safely.
Prior systems include those where a pressurized gas has been used to force molten material from a container of molten lead out a spout. One such device employs measurement of the velocity of molten metal flowing through a spout as the determining factor, as shown in U.S. Pat. No. 3,675,911 issued Jul. 11, 1972 to Kapun for "Arrangement For Discharging Predetermined Amounts Of Molten Metal From A Vessel". Another employs a pair of reference electrodes spaced along one side of an outlet passage in the delivery spout, metal flowing between the two electrodes indicating that the level of molten metal has reached a certain height within the spout. Shot timer means are connected to the reference electrode and are activated when the molten metal has reached the predetermined height. This system is described in U.S. Pat. No. 3,876,191 issued Apr. 8, 1975 to Lauersdorf for "Furnace Ladling Apparatus And Crucible".
A device of the overflow variety is described in U.S. Pat. No. 4,289,193 issued to Stamp on Sep. 15, 1981 and entitled "Accumulator Plate Assembly Methods". This device includes a mold having a number of separate cavities arranged on either side of a duct. A weir is positioned between the duct and the individual mold cavities, the weir determining the level of lead to be poured. The lead pumped into the duct flows into the cavities over the weir. Once the casting operation is completed, lead from the duct flows back to the source pump, and an overflow return system is employed to maintain a constant level of lead in the duct after the mold cavities have been filled. The system includes an exit passage formed in the end of the duct near the air flow pump. A special valve cycling arrangement causes lead to be sucked back into the duct below the level of the weir. The level of lead in the duct then falls below the top of the weir, thereby causing the level of lead in the cavities to fall to the level of the top of the weir. After filling of the individual cavities, the battery plates are lowered by rams and are partially immersed. Due to the flow of cooling water into the cooling molds, the lead rapidly solidifies and is cast onto the lugs.
Systems are also known which use weighing devices for measuring the amount of molten material See Bengt et al. U.S. Pat. No. 3,834,587 issued Sep. 10, 1974 for "Means For Automatic Control Of Batching When Casting From A Heat-Retaining Casting Furnace Or Ladle (Crucible)". The batching ladle is weighed and the output signal of the weighing system is fed to a deriving device which controls the tapping of the furnace by control of output of air into the melting crucible.
A system employing air pressure and a bubbler tube is shown in U.S. Pat. No. 3,499,580 issued Mar. 10, 1970 to Smith for "Pressure Pour Apparatus And Component Thereof". A cushion of gas from a regulated pressure source aids gravity in maintaining a constant head to force liquid out through the pouring orifice.
Mechanical plungers are used in U.S. Pat. No. 703,420 issued Jul. 1, 1902 to Hunter for "Process Of Making Electric Accumulator Plates" and U.S. Pat. No. 1,747,552 issued Feb. 18, 1930 to Lund for "Grid Casting Machine". Mechanical pistons are also used in U.S. Pat. No. 4,158,382 issued Jun. 19, 1979 to Oxenreider et al. for "Apparatus For Casting Lead Into Plastic For Side Terminal Batteries", U.S. Pat. No. 4,284,122 issued Aug. 18, 1981 to Oxenreider et al. for "Method And Apparatus For Casting Lead Into Plastic For Side Terminal Batteries" and U.S. Pat. No. 2,735,148 issued Feb. 21, 1956 to Shannon et al. for "Process For Casting Storage Battery Straps And Terminals".
Other metal dispensing furnaces which employ air pressure are shown in U.S. Pat. No. 3,510,116 issued May 5, 1970 to Harvill et al. for "Metal Dispensing Furnace". In this patent, an inert gas supply is used to force air over a weir into a receiving area. A pouring spout which is inclined, is adapted to feed the molten lead into the mold cavity. A baffle separates a surge chamber and the dispensing chamber and is configured in such a way that upon release of the air pressure, a back flow of molten metal maintains a clearance between the two chambers resulting in agitation.
All of the aforementioned devices suffer from one or more disadvantages when applied to the large scale manufacture of castings, especially when casting straps in the manufacture of lead-acid batteries. The mechanical systems can foul and repair to the sliding components is time consuming and expensive. The devices which use high pressure air are also ineffective in producing precise quantities of lead. The system which uses the overflow from a duct into cavities across a weir requires complex valving for the pumping operations, and the duct system employed for maintaining the level of molten metal in a proper fluid state and at the proper level is complex and subject to periodic failure.
A system for pouring accurate amounts of molten metal, such as pouring accurate amounts of molten lead for battery strap casting operations, would represent a significant advance in the art.